When I try to download a video "download this video" button does not appear. How to solve this problem?

The problem has been fixed in IDM version 6.42 build 33

The solution is to update IDM to version 6.42 build 33.

You may use "Help->Check for updates..." menu item to update IDM. Or you may download IDM 6.42 build 33 and install it over your current version. Please note that all IDM settings and downloads will not be affected by using these types of updates.